This invention relates generally to a capillary tube assembly which connects an atmospheric pressure ionization chamber to a lower pressure mass analyzer assembly, and more particularly to a capillary assembly having a removable capillary tube.
When an atmospheric pressure ionization (API) source such as an electrospray (ES) or atmospheric pressure ionization (APCI) source is installed on a mass spectrometer system, the gas flow from the atmospheric pressure ionization chamber into the vacuum system of the mass spectrometer must be set to match the pumping capacity of the vacuum pumps used. Small diameter orifices and capillary tubes are the two methods most often used to limit the gas flow from the atmospheric pressure spray chamber into the vacuum system of the mass spectrometer. These capillary tubes are often heated to provide thermal energy to the solvated ions passing through them, thus desolvating these ions.
Non-volatile material from the samples being analyzed by the mass spectrometer system can accumulate at the entrance or on the inner bore of these capillary tubes. These non-volatile materials can be salts from the liquid mobile phase being sprayed into the atmospheric pressure ionization source. They can also be proteins, lipids or salts, remaining in the sample solution after extraction from biological fluids such as plasma or urine. The accumulation of non-volatile material on these capillary tubes can lead to a reduced transfer of ions and reduction of signal. This requires the user to clean the capillary tube or replace it with a new one. Capillary tube maintenance or replacement typically occurs every several months for complex samples, and yearly for clean samples. Whatever the frequency of maintenance, the fact remains that the system is vented. The time for maintenance and bringing the mass spectrometer system back online takes approximately one day. This means a low sample throughput which translates into loss of revenue for a laboratory.
It is an object of the present invention to provide a heated capillary assembly in which the capillary tube can be easily and quickly removed from its heater for inspection, cleaning and replacement.
It is another object of the present invention to provide a heated capillary tube assembly with a replaceable capillary tube in which venting of the mass analyzer system is restricted during capillary tube removal and replacement.
These and other objects of the invention are achieved by a system in which an atmospheric pressure ionization chamber is connected to a lower pressure region of a mass analyzer via a capillary tube assembly having a removable capillary tube and to a system which inhibits venting of the lower pressure region during removal and replacement of the capillary tube.